1. Field of the Invention
The present invention relates to an image-forming apparatus and, more specifically, to a guide, arranged upstream to a transfer device for electrostatically transferring an image to a sheet-like material, to which a bias voltage is applied.
2. Description of the Related Art
Many kinds of image-forming devices have an electrostatic transfer device which transfers a toner image from an image-bearing member, e.g., a photosensitive drum, to a sheet-like material, e.g., a paper sheet. In these image-forming apparatuses, a transport mechanism transports the sheet-like material to the transfer device one by one, and the sheet-like material is supported by the transport mechanism when the transfer device transfers the toner image. If the transfer mechanism which the sheet-like material contacts when the toner image is transferred, is made from an insulating material, the transfer mechanism stores an electric charge which is provided by the transfer charger or is caused by friction between the transfer mechanism and the sheet-like material when the humidity is low. Therefore, the transferred image may not be of high quality due to the influence of the stored electric charge. Also, the stored electric charge attracts toner floating in the air, and the attracted toner makes the back of the sheet-like material dirty.
On the other hand, if the transport mechanism which the sheet-like material contacts when the toner image is transferred, is made from a conductive material coupled to a ground potential, the transfer charge from the transfer device leaks to the ground potential through the sheet-like material and the transport mechanism when the humidity is high. Therefore, the transferred image may not be of high quality.
In this way, recently, an image-forming device which may form a high quality transferred image irrespective of the humidity, is requested.
As one structure which responds to this request, a transport mechanism to which a bias voltage is applied is disclosed by Japanese Patent Publication No. 61-32667.
This structure, however, has a problem. That is, toner is attracted by a non-contact portion of the transport mechanism which the sheet-like material does not contact when the sheet-like material is transported. Therefore, when a large size sheet-like material is transported after a small size sheet-like material is transported, the attracted toner makes the back of the large size sheet-like material dirty.